In recent years, nephritis induced by BK virus (BKV), a non-enveloped double-stranded DNA polyomavirus, has become a severe problem after renal transplantation. There is a critical need to better define the molecular mechanisms of BKV entry into its target cells and to develop efficient treatment strategies for BKN. An objective of the proposed study is to identify the protein component of the BKV receptor and to develop pharmaceutical agents capable of mitigating BKV entry into human renal proximal tubular epithelial cells (HRPTEC), considered to be one of the main natural targets of BKV. The identity of the BKV receptor is unknown. At present, no specific pharmacological agent preventing BKV nephritis is available. Currently, the only efficient therapy against BKV nephritis appears to be a reduction/change of immunosuppressive agents, and this may increase the inherent risk of rejection. In our preliminary studies we have established that caveolar endocytosis is critical for BKV infection of HRPTEC and revealed several important steps of the BKV intracellular trafficking pathway in HRPTEC. Furthermore, our data suggest that the antagonist of Endothelin-1 binding to Endothelin B receptor (ETRB) prevents BKV infection of HRPTEC. Endothelins (ET), agonists of G- protein coupled receptors; act as important mediators of renal disease progression. Our working hypothesis is that binding of BKV to ETRB in HRPTEC is the critical step in the BKV entry into HRPTEC and that ETRB antagonists can be efficient as agents against BKV nephritis. Specific Aim 1 will test the hypothesis that N- linked glycoprotein ETBR serves as a receptor for BKV particles in HRPTEC. To establish that ETRB serves as the binding molecule for BKV particles in HRPTEC, siRNA mediated silencing of the ETRB gene will be employed. We will also carry out experiments to determine direct association between ETRB and BKV particles and evaluate necessity for ETRB presence for BKV infection. BKV infection will be detected using the following markers: the percentage of infected cells, as detected by immunofluorescence, the cellular levels of BKV large T antigen expression, as detected by western blot analysis and viral load, as detected by real-time PCR. Proposed study will provide the basis for a novel strategy for therapeutical intervention in BKN, ultimately improving long-term graft survival after renal transplantation. PUBLIC HEALTH RELEVANCE: In recent years nephritis induced by BK virus (BKV), non-enveloped double-strand deoxyribonucleic acid polyomavirus, has become a severe problem after renal transplantation. Polyomavirus nephropathy, also termed BK-virus nephropathy (BKN) affects 1% to 10% of all kidney transplant recipients and is emerging as an escalating threat. Since graft loss due to BKN ranged from 10% to more than 80% in kidney transplant recipients with BKN there is a critical need now to better define the molecular mechanisms of BKV entry into its target cells and to develop efficient treatment strategies of BKN. The identity of the BKV receptor is unknown and no specific pharmacological agent preventing BKV nephritis is available. This proposal will uncover the protein component of BKV receptor and provide the basis for a novel strategy for therapeutical intervention in BKN to ultimately improve long-term graft survival after renal transplantation.